There are three (3) modulation busses, two of which are assigned to the modulation and pitch wheels.

1. CV & MOD BUSSES.

Mod Wheel Buss.

Modulation Sources:

1. The square output of the LFO
2. The triangular output of the LFO
3. The upwards sawtooth output of the LFO
4. The downwards sawtooth output of the LFO
5. S&H
6. Oscillator 4
7. External In 1
8. External In 2
9. Env (the envelope from VCF1)

Specifies how much the modulation wheel affects the modulation between source and destination.

LFO rate: this ranges from something like 0.05 Hz to ~45 Hz. It seems to me that, in the way Ha-Jo has designed it, most of the LFO’s “resolution” is between 1 and 7, i.e. this LFO knob is especially suitable if you want to be precise in adjusting slow (or ultra slow for that matter) sweeps. The easily audible results occur from 7 to 10. It’s like this:

1 2 3 4 5 6 7 8 9 10
Ultra slow………………………………………… Slow………………Very fast

I am not sure yet if I like this design. On the one hand you have lots of nice resolution from ultra-slow to slow and on the other hand it’s a bit difficult to adjust the rate between 7 and 10.

Mod. Fix Buss.

Modulation Sources:
Same as above

Modulation Destinations:
Same as above

Mod. Fix Range:
Specifies how much this knob affects the modulation between source and destination.

RND Rate: Basically the S&H rate. Needs more range and tweaking as it seems that up till 8 or 9, it doesn’t seem to do anything.

Pitch Wheel Buss.

Modulation Sources:
1. VCO2 + VCO4
2. VCO1 – VCO4 (all VCOs)

Modulation Destinations:
Same as above

Pitch wheel range:
Specifies how much the pitch wheel affects the modulation between source and destination.

Velocity switch:
The Challenger responds to your playing dynamics by routing velocity either to Filter 1, Filter 2 or both Filters. This is a fixed amount and it produces nice results (it’s neither nervous nor weak). Should you want to vary the amount, you can always concoct some external logic by using the CV velocity output into an attenuator and back into the CV filter input (labeled Filter pedal 1). I have tried this with my Moog VX-351's attenuator and it works as expected.

There are 4 VCOs in the Challenger. Each VCO has controls for
a. Range
b. Tune
c. Modulation
d. Waveform

The “Range” selector has the typical settings of 32’, 16’, 8’, 4’, 2’ and 1’ plus an additional “LO” setting for the 4th VCO which makes it function as a LFO. The 4th VCO also appears as a modulation source in all three modulation busses.

The “tune” knob is used well… to fine-tune each oscillator. And with the Challenger being a pure analog synth, you get a smooth zip when you adjust this parameter, no nasty semitone quantization here.

The “modulation” knob adjusts the amount of modulation that affects the VCO.

The “waveform” selector is used to select between the available waveforms which include:
1. sine
2. triangle
3. saw
4. square
5. pulse with a pulse-width cycle of 25% and another
6. pulse waveform with a pulse-width cycle of approximately 10%.

At the bottom of the oscillator section there exist 5 switches. From left to right we have:
a. Soft sync between oscillators 1 and 2. The amount is adjustable from the dedicated “modulation” of VCO1. Soft sync is already tame by nature, since it’s the harmonics which are being synced and not the fundamental frequency. Soft sync on the Challenger sounds very nice - it’s more prominent than the soft sync found in the Andromeda (which most of the times doesn’t seem to do a lot) and it produces a mild swirling timbre. Edit: it's also possible to have SoftSync and Ring Modulation simultaneously but not much will happen. Ring Modulation produces the sum and the difference of the original signals (without the originals being present in the output). If Softsync is turned on then it will try to sync all the harmonics. So for any given harmonic, if the original signals are let's say f1 and f2, then with soft sync f1 will be the same as f2 (or at least very close). So, with ring modulation the difference will be: f1 - f2 = 0! In other words the ring modded signal is likely to produce just the sum of the original signals and not their difference, thus Ring Modulation doesn't sound like Ring Modulation anymore.
b. FM/PWM for all oscillators. This demands some explanation as it left me scratching my head. FM is not actually FM, but pitch modulation. Pitch might be synonymous with frequency, but labeling it FM might cause confusion to some people who will see FM and will think that this is DX7 territory. It’s not. So let’s give an example. Let’s say we want the LFO to modulate VCO1’s pitch. We have these steps:

1. In the Modulation section, we choose which buss of the 3 we want to use. Let’s say we want the Mod.Wheel Mod Buss so that we can fade in the effect by using the Mod Wheel.
2. Modulation Source = triangle wave
3. Modulation Destination = Osc
4. Modulation range = 7
5. In the Oscillators’ section, we switch on FM/PWM.
6. In VCO1, we increase the modulation and we hear the LFO modulating the pitch of VCO1.

PWM was not available in the prototype and Ha-Jo implemented it after my request. To have PWM on a VCO we need to make sure that the waveform of that VCO is set to Pulse 10% AND the respective modulation knob is set to 0, otherwise we will hear both PWM and pitch modulation simultaneously. So to have PWM on VCO1 we have these steps:

1. In the Modulation section, we choose which buss of the 3 we want to use. Let’s say we want the Mod.Wheel Mod Buss so that we can fade in the effect by using the Mod Wheel.
2. Modulation Source = triangle wave
3. Modulation Destination = Osc
4. Modulation range = 7 (in this case adjusts the depth of the PWM)
5. In the Oscillators’ section, we switch on FM/PWM.
6. In VCO1 we set the modulation knob to 0.

c. Hard Sync between oscillators 3 and 4 with VCO3 being the master oscillator and VCO4 being the slave oscillator. In order for Hard Sync to function properly the FM/PWM switch must be set to “on” and “Hard Sync” must be set to “on”, too. Hard sync can be made to fade in and out by using either the pitch wheel or the mod wheel. Hard sync and Cross modulation between VCOs 3 and 4 are mutually exclusive which means that it’s either one or the other but not both at the same time.
d. Cross modulation (X-mod) between oscillators 3 & 4, useful for introducing a little grit or just to make the sound very inharmonic and dissonant.
e. The last switch enables/disables tracking of VCO4 from the keyboard, i.e. decoupling.
f. There is also Ring Modulation between oscillators 1 and 2 but the respective knob is found in the mixer section, because the RM signal can be mixed to taste and sent to either VCF1, VCF1 or both. The RM in the Challenger sounds very nice, definitely capable of producing some characteristic clangorous timbres courtesy of RM.

In an email Ha-Jo told me that the oscillators are designed after the oscillators in the Formant modular but with better properties. Both oscillators and filters are designed with opamps and OTAs (no special ICs whatsoever). To my ears they sound very rich and raw. Initial impressions are that they are richer in harmonic content than the ones found in the Voyager. The sawtooth and pulse waveforms, especially, have this buzzing and electrifying quality which is the territory of vintage synthesizers. Send a single VCO into VCF1, medium resonance, and mess around with the cutoff. When open wide it has the aforementioned “electrifying” quality (that I usually associate with Oberheims), when closing the filter it sounds unbelievably warm and juicy. The filter sweeps are delightful! I must have spent at least one hour being in aural ecstasy, just messing with the cutoff.

The other two pulse waveforms also sound very nice. I was able to able to synthesize funky clavinet leads and other paranormal phenomena in zero time, lol.

Having a sine waveform available in the oscillators is a very welcomed feature: tuning it one octave lower than the rest of the VCOs (i.e. using it as a sub-oscillator) and sneaking it into the mix, makes the Challenger sound ridiculously fat with absolutely no sense of shame, lol.

3. MIXER / ROUTER

Four different knobs enable each of the associated oscillators to be mixed with each other prior to hitting the filters. There is also provision to mix the ring modulated signal of VCOs 1 and 2, an external signal (accompanied by an Overload LED) and/or noise (white/pink selectable from the lovely blue switch). The two noise colors sound as they should; sending them to the filters produces all kinds of seas and howling winds heh

There is a dedicated selector switch available to all of the sound generating sources which enables them to be routed either to VCF1, VCF2 or VCF1+VCF2, with this being essentially a parallel configuration.

There are also two tiny knobs labeled MIDI 1/Learn and MIDI 2/Learn that indicate MIDI activity, either when played as a single mono synth (Channel 1) or when played as a dual mono synth (Channels 1 and 2). The Challenger can function as a duophonic synthesizer, i.e. 2 voices of polyphony when it's played from its own keyboard or it can function as a dual mono synth when played from its own keyboard and from MIDI simultaneously. In this case 1 voice allocated to the lower part (channel 1) and 1 voice allocated to the upper part (channel 2).

4. FILTER BANK

There exist two VCFs in the Challenger.

Filter 1 is a multimode filter with the following outputs which can be selected from the dedicated selector:

There are two switches to enable the filters to be tracked from the keyboard. I would much prefer a knob here to adjust the amount of tracking and have brought this to Ha-Jo’s attention. He said that he considered it too, but somehow it didn’t produce satisfactory results. However mourn not, as there is a workaround: Route the output of the CV-pitch into an external attenuator (Moog CP-251 anyone?) and back into the CV input of the filter(s), and you have variable tracking.

Both filters can self oscillate and produce a sine wave at the specified cutoff frequency. As a result I was able to synthesize punchy kick drums very easily. A little while ago I was debating that it might not be preferable to crank the resonance to maximum, as I have found that it oftentimes thins the sound too much. This is not the case with the Challenger however; the resonance needs to be at 10 to get the desirable thud. Other settings for resonance can also be used [8..9] but with these settings the kick has less power, which might be preferable in some cases.

In the Filter section there are two dedicated ADSR envelopes for each of the filters. Envelopes are analog, with very fast attack times and can be inverted by using the respective blue switches.

5. LOUDNESS / PANORAMA

The last section of the Challenger has two VCAs and two ADSR envelopes for these. There are controls for specifying the pan position of the VCAs and two selectors to specify how the pan-modulation is applied.

The settings, which are identical for both VCAs 1 and 2, are:
1. Manual (in which case the knobs above become active).
2. Mod wheel (so that you can control the pan with the Mod wheel).
3. Pitch wheel
4. Mod Fix
5. Key Follow (pan depends on the key that is pressed).

Knobs for volume, headphones’ volume, a 440Hz reference tone switch and the green On/Off switch complete the picture of this section.

6. MOD & PITCH WHEELS

Except for the Pitch and Mod wheels, there exist six push buttons.

1. Channel
2. Transpose
3. Program (used to program the built in MIDI/CV converter)
4. Control (used to program the MIDI/CV converter) Edit: Aftertouch can be programmed from here.
5. Down: decreases the value of whatever is selected by 1.
6. Up: increases the value of whatever is selected by 1.

Edit: The internal MIDI/CV converter can be programmed from the front panel to function as follows:

* High Note priority
* Last Note priority
* First Note priority
* Single Trigger - in this mode you can play legato.
* Multi Trigger - legato not possible.

7. REAR PANEL

From left to right:

1. Power socket
2. Right Output
3. Left Output
4. Stereo Output
5. Pedal Loudness – used to control the amplitude of the VCAs
6. Pedal Filter 2 – (Of course it doesn’t necessarily need to be a pedal per se; CV from an analog sequencer or LFO can be perfectly be usable here - I have tested it with the Moog CP-251 and it works as expected)
7. Pedal Filter 1 – (same as above)
8. Low External In – when in duophonic/dual mono mode, this is used to send signals into Filter 1. I have routed the output of the headphones into the Low external In input and adjusted the respective knob in the Mixer/Router section. Instant feedback and boy does it sound good! If you want to have a little grit or to just completely mess up the signal it's all here!
9. High External In – same as above, but now filter 2 is used.
10. Mod In - I need to ask about this. Stay tuned.
11. Mixer Out – (this is the output of the signals prior to hitting the filters, in case someone wants to process/filter the Challenger externally)
12. Gate Input – self explanatory: a +5v signal can trigger the envelopes.
13. CV Velocity Input -
14. CV Pitch Input
15. Gate Output – a +5v signal occurs at this output whenever the envelopes are triggered.
16. CV Velocity Output
17. CV Pitch Output
18. MIDI In 1 – for the “lower” part (VCOs 1&2, VCF1, VCA1)
19. MIDI In 2 – for the “upper” part (VCOs 3&4, VCF2, VCA2)
20. MIDI Out. If you want to play the Challenger duophonically you can use a MIDI cable from MIDI Out to MIDI In 2 and voila, you have 2 voices.

Miscallenous Stuff.

Stay tuned.

Last edited by OurDarkness; 16th February 2011 at 12:42 AM..
Reason: Corrected a few things

glad the project is going forward, and the challenger finally started shipping. when you have time, could you please make some nice demos... with filter sweeps, no resonance, with resonance etc.. filter env.. pwm.. the works...

yeah and more detailed pictures of the whole control panel would be most welcome too to see everything this beast has up its sleeve..

glad the project is going forward, and the challenger finally started shipping. when you have time, could you please make some nice demos... with filter sweeps, no resonance, with resonance etc.. filter env.. pwm.. the works...

yeah and more detailed pictures of the whole control panel would be most welcome too to see everything this beast has up its sleeve..

Dude, you were right about the VCOs. They are SCARY. I have spent one hour sending just a single sawtooth into the 12dB filter and messing around with the cutoff. It's freakingly good.

I took some detailed photos of the front panel but was too tired/excited to upload them yesterday. I started at 15:00 and ended at 03:00, lol.

I'd like your thoughts on a direct comparison of the two if possible...

Yes, I have a Voyager. Challenger and Voyager will have their signals mixed very soon.heh

First impression is that the Challenger's oscillators and filters are devastating. Much as I like the Voyager, the sound is different. The Challenger is raw, aggressive and electrifying. Voyager's tone is more well-behaved and round. Different flavors, as always.

Yes, I have a Voyager. Challenger and Voyager will have their signals mixed very soon.heh

First impression is that the Challenger's oscillators and filters are devastating. Much as I like the Voyager, the sound is different. The Challenger is raw, aggressive and electrifying. Voyager's tone is more well-behaved and round. Different flavors, as always.

Καλορίζικο! I was looking for a comparison between the Challenger and the Voyager...Are they comparable in build quality? Challenger's aesthetics remind me some cheap chinese products...(golden screws for example...) Of course, i might be very wrong...How does it feel?